Thank you to everyone who shared their view and experience on this topic.
I booked my flight through AMEX Travel website (as I have been doing for the past 3 years) but I don't recall seeing the Jetstar symbol against the flight when I made the booking.
Being a busy business traveller who's always flown QF flights domestically and internationally, it is easy to overlook the subtlelity of QF/JQ arrangement, the fine prints provided by a hyperlink, etc. I wonder how many frequent flyers actually read all the terms and conditions of a flight ....
Like someone said, it is a lesson I learnt the hard way. I also concur with those who think QANTAS could have unintentionally put non Frequent Travellers at a disadvantage through this 'misleading' practice.
However, I am still indignant about the exhorbitant profit that QANTAS made at my expense. Don't they have a Duty of Care to the QF-fare customers or are the fine prints and hyperlinks sufficient?